The present invention generally relates to the process of isotope separation, by which atoms of varying molecular weight can be differentiated.
Commonly-owned U.S. Pat. No. 6,614,018 to Schubert discloses an apparatus and process for continuous isotope separation in microgravity using solar power. Generally, Schubert's apparatus has axial symmetry and utilizes magnetic beam confinement to perform a continuous process in microgravity environments.
Several subfields relate to apparatuses and processes of the type taught by Schubert. One subfield is mass spectroscopy, wherein a sample is ionized and sputtered from the matrix being studied through bombardment by another ion such as oxygen or argon. A sample analyzer segregates isotopes through the application of a magnetic field. As ions of charge q, with a velocity v and mass m pass through a magnetic field of strength B, they experience a force perpendicular to the field direction according to the Lorentz force, F=qvxB (F is force vector, a is acceleration, m is mass, q is electron charge, v is velocity vector, B is magnetic field strength, and x is the cross product operator). This force causes an acceleration in a direction normal to the original velocity according to Newton's law a=F/m (a is acceleration and m is mass). Because different ions have different masses, the acceleration they receive is different. This effect is exploited to separate out the various elements and isotopes of the matrix under study. Suitable collectors monitor the amount of charge impinging at the location associated with various isotopes, providing an indication of their presence, and an approximate indication of their relative abundance. Previous work in the field of mass spectroscopy include U.S. Pat. No. 4,066,895 to Iwanaga, U.S. Pat. No. 4,174,479 to Tuithof et al., U.S. Pat. No. 5,220,167 to Brown et al., U.S. Pat. No. 3,443,087 to Robieux et al., and U.S. Pat. No. 3,772,519 by Levy et al. This technique of magnetic separation is widely used in many fields, as will be discussed below
In the field of ion implantation, used typically for semiconductor manufacture and for impregnation of specialty materials, a gaseous molecule containing the element of interest is ionized using a radio frequency plasma. The plasma field causes dissociation of the molecule, and causes an excited state of the element to be implanted. All excited species of charge q are then accelerated using electrostatic fields of strength E according to the equation F=Eq. The accelerated ions are collimated and passed through a magnetic field to separate the various isotopes. A suitable shutter system is employed to select the ion of interest, which is then allowed to proceed toward the substrate to be implanted with this ion. However, along the beam path, between the separation magnet and the substrate, dynamic electric fields, oriented typically in two perpendicular directions to the beam axis, are employed to deflect the beam slightly. This deflection is used to cause the beam to be scanned across the substrate, typically with the desire to uniformly cover the substrate area. Once the beam arrives at the substrate, typically with a relatively high velocity and relatively low density, the ions will impinge upon the surface, and penetrate to a distance determined by the beam energy, the ion mass, the angle of incidence, and the atomic mass and crystal orientation of the substrate. Several patents in this area include U.S. Pat. No. 4,841,143 to Tamura et al., and U.S. Pat. No. 5,751,002 to Ogata et al.
Isotope separation, as a field of study, is principally used to enrich uranium with the isotope of atomic weight 235, relative to the much more abundant U238. A number of patents in this field demonstrate a wide variety of techniques for achieving isotope enrichment, such as U.S. Pat. No. 3,935,451 to Janes, U.S. Pat. No. 3,940,615 to Kantrowitz, U.S. Pat. No. 4,202,860 to Miyake et al., U.S. Pat. No. 4,726,967 to Arendt et al., U.S. Pat. No. 5,024,749 to Snyder et al., U.S. Pat. No. 4,399,010 to Lyon et al., U.S. Pat. No. 5,422,481 to Louvet, U.S. Pat. No. 4,757,203 to Gil et al., U.S. Pat. No. 5,224,971 to Mukaida et al, and U.S. Pat. No. 3,953,731 to Forsen. Among the various techniques are those which use a linear direction of ion travel, and those which employ a spiral or cyclotron ion movement. In all cases, the uranium, or other element, such as zirconium, is first ionized using one of several different methods. The first broad class of ionization techniques involves first evaporating the material, and then ionizing it using radio-frequency (rf) energy or tuned laser radiation. Evaporation is accomplished with any of several techniques, such as Joule heating, laser bombardment or ion sputtering. Ionization with rf energy will typically excite all isotopes of the element of interest. However, with laser ionization, the frequency of radiation can be selected to preferentially ionize one isotope over another. This appears to be the preferred method in many patents, since it allows separation to be accomplished using electric fields, instead of magnetic fields, although both can be found in the patent records. Once the moving (linear or cyclotron) isotopes are ionized and separated by either electric or magnetic fields, they are collected at surfaces that are temperature controlled to allow condensation.
The application of very rugged coatings of metal or ceramic is the goal of thermal spray. In each form, the material to be deposited is supplied in a powdered form carried in a stream of gas, such as nitrogen. The small particles of material are plasticized, melted, or ionized, depending on the energy supplied. This energy may be from the combustion of a reactive fuel with oxygen or from an electric arc. The heated particles of metal or ceramic are then carried to the substrate to be coated by the carrier gas, or by the velocity of the exit gasses from combustion. These particles then coat the surface of the substrate, preferably with very little surface reaction, and typically produce a very dense coating. Representative patents in the field of thermal spray include U.S. Pat. No. 3,892,882 to Guest et al., and U.S. Pat. No. 5,716,422 to Muffoletto et al.
The principles of magnetohydrodynamics involve the motion of a charged medium through a magnetic field. In a typical embodiment, the momentum of the moving medium imparts a backward electromotive force which can be used for power generation. In another form, the magnetic field can be used to selectively alter the trajectories of the moving medium, which may be a plasma of ionized isotopes, for example. In this way, magnetohydrodynamics is similar in principle to mass spectroscopy. A patent describing this method is U.S. Pat. No. 4,737,711 to O'Hare. This patent also describes a method of element separation.
A materials processing environment in a circular orbit around a massive body is essentially in a free-fall, where the effects of static gravity, such as those felt on the surface of such a massive body, are not felt or are very small. Such a microgravity environment has certain advantages for materials processing. The sedimentation or settling of materials of varying densities in a suspension does not occur, allowing the formation of more homogenous materials in orbit than on the surface of a planet or planetoid. The relatively less stringent requirements for fixturing are another feature exploited in some patents on microgravity processing. A sample of microgravity processing patents is U.S. Pat. No. 5,196,999 to Abe.
Many methods for the separation of chemical elements or molecules in space have been proposed and studied. For the most part, these include the use of reagents, catalysts, and consumable chemicals which must be brought from a planet such as Earth, at great expense. Furthermore, the equipment for these processes tends to be very expensive and intricate, requiring significant maintenance. References to such schemes can be found in U.S. Pat. No. 4,737,711 to O'Hare (noted above), U.S. Pat. No. 5,374,801 to Leung, and U.S. Pat. Nos. 5,096,066 and 5,153,838 to Kindig.